Isolated rhesus monkey luteal cells offer a model system for the in vitro study of primate corpus leuteum function and assessment of the direct influence of various factors on the corpus during its lifespan. Initial topics of interest in this project have included 1) Morphological and functional correlations between the intact corpus luteum and subsequent isolated luteal cells, 2) Comparison of the in vitro steroidogenic potential of luteal cells obtained from corpora lutea at various stages of the menstrual cycle and pregnancy, and 3) evaluation of the influence of potential luteotropic and luteolytic agents on in vitro steroidogenesis of macaque luteal cells. Current research indicates that prostaglandins may be luteotropic in "young" corpora lutea, but that the "aged" luteal body produces less progesterone in the presence of prostaglandins. Further, progesterone production which is stimulated by HCG is negated by prostaglandins when using cells obtained from the late pregnancy, rejuvenated corpus luteum.